This invention relates to gas analysis, and more particularly to an improved method and apparatus for determining the amount of a sample gas reacting with an electrolyte.
In the field of air pollution control it is necessary to measure the amount of pollutant in an exhaust gas stream. For example, it may be necessary to measure the quantity of noxious sulfides or sulfur dioxide in exhaust gases of factories or refineries.
A variety of ways are presently known by which the concentration of pollutant in a sample gas stream can be analyzed through redox reactions between the sample gas and an electrolyte. Generally speaking, the prior art electrolytic monitoring systems fall within two categories -- those known as galvanic cells in which the electrical potential between the electrodes is provided by a self-contained source, and cells in which the potential between the electrodes is generated by an external power source.
The current flow between the electrodes in either a galvanic or an externally powered cell is proportional to the amount of reactant gas flowing in the system. In one commercial galvanic apparatus for measuring reducing reactant gases, an external electrical power supply generates free halogen at a predetermined rate, and the resulting signal level is monitored by a galvanic system. When a reactant gas is admitted to the apparatus, the decrease in signal level is a measure of the reactant concentration. Since galvanic systems are limited in the amount of electrical current they can produce, they are inadequate in analyzing sample gas streams containing high concentrations of reducing reactant gases.
In contrast, external power systems are not limited in their capacity to generate sufficient electrical energy to monitor the contents of sample gas streams containing a relatively large concentration of reactant gas. However, such monitoring systems in the past have been relatively complex because they have been comprised of three or more electrodes and elaborate hardware which make such systems relatively costly to produce and operate, together with being difficult to operate and being lacking in versatility.